1. Field of the Invention
The present invention relates to a multi-fuel injection system for an internal combustion engine having a plurality of cylinders. More particularly, the present invention relates to a fuel injection system for a diesel engine in which is used a main fuel such as an alcohol fuel having a poor self-ignitable property and an auxiliary fuel such as a diesel fuel having a good self-ignitable property.
2. Description of the Related Art
It is known in the art that, in the multi-fuel injection system, the alcohol fuel and the diesel fuel are preferably injected in a stratified manner without substantial mixing. To this end, a minor ignitable fuel is first injected to provide a kindling fuel, and then the main alcohol fuel is injected.
U.S. Pat. No. 4,416,229 discloses a fuel injection system for a diesel engine having a single injector for injecting diesel fuel and alcohol fuel into each combustion chamber of the engine in the form of a plume having diesel fuel at its tip, so that the diesel fuel is ignited by the compression in the chamber and the alcohol fuel is ignited by the ignition of the diesel fuel. The fuel injection nozzle has two fuel inlet passages formed therein to introduce the respective fuels, which fuels meet near the valve seat. The diesel fuel is delivered into the nozzle space under a pressure below the nozzle opening pressure, to replace the alcohol fuel therein and to fill the space at a timing between consecutive fuel injection timings at which the alcohol fuel is injected under a pressure sufficient to open the nozzle.
U.S. Pat. No. 4,481,921 and the corresponding Japanese Unexamined Patent Publication Nos. 58-206,859 and 58-206,867 disclose a fuel injection apparatus having fuel injection nozzles similar to those disclosed in the U.S. Pat. No. 4,416,229.
To compressively deliver the two kind of fuels under different pressures, it is necessary to provide two different fuel injection pumps. For this purpose, U.S. Pat. No. 4,416,229 has two fuel injection pumps having a plurality of fuel outlets, respectively. U.S. Pat. No. 4,481,921 has a fuel injection pump having a plurality of fuel outlets for alcohol fuel and a plurality of fuel compressors having respective fuel outlets for the diesel fuel. In both cases, fuel are delivered into the fuel injection nozzles through the specific fuel outlets having a fixed relationship relative to that nozzle. Therefore, the delivered diesel fuel, which may be fundamentally small in volume, may vary between the cylinders of the engine due to manufacturing errors in the individual elements.
Since the diesel fuel is to be delivered in small amounts under a relatively low pressure, it would be desirable to construct the fuel injection pump for the diesel fuel using a far simpler design. In this regard, the above-referenced U.S. Pat. No. 4,481,921 uses fuel compressors having a very simple design, which are driven by the pressure of the alcohol fuel injected by the main fuel injection pump. However, in this design each cylinder of the engine must be equipped individually with a compressor and thus the connections between the compressors, main fuel injection pumps, and nozzles are complicated.